The objectives of this research proposal are to determine the sequence of events involved in the development and functioning of a chemotactic signalling system and to discern the role of cell movement in the expression of specialized cell functions. This problem will be approached by a combined genetic and biochemical study of the major membrane-mediated events involved in chemotaxis in D. discoideum amebae. The specific membrane components to be investigated are adenylate cyclase, (the enzyme which synthesizes cAMP, the chemotactic agent in this system) and the cell surface cAMP receptor, which mediates cellular responses to external cAMP. We will continue our current investigations of the regulatory elements which alter the levels of these membrane components with particular consideration of the role of specific intercellular contacts. Many of our studies will be aided by the various mutants which we have isolated and partially characterized. They have already provided important insights into the sequence of events involved in chemotaxis and cell differentiation. We will continue our study of these mutants, using both biochemical and genetic techniques, and search for other mutants defective in the chemotactic system.